The present invention relates to pipe joints and couplings and, more particularly, to a joint for coupling corrugated plastic pipe segments.
Plastic pipe is often used to reline worn concrete or tile pipes, such as sewer pipes. It is desirable for such liner pipes to have annular protrusions such as annular corrugations or ribs extending radially from their outer surfaces and axially spaced along their lengths to strengthen the wall of the pipe. Such protrusions may also take the form of a helical corrugation or helical rib spiralling axially along the outer surface of the pipe.
It also is desirable for such liner pipes to have a uniform outer diameter so that the liner pipe can be inserted through or pulled through sewer pipes without edges or projections snagging on or hanging up on protrusions on the interior surface of the pipe or casing to be relined. Therefore, it is preferable to provide a joint for coupling two ends of plastic liner pipe segments which has the same outer diameter as that of the liner pipe segments to be joined.
U.S. Pat. No. 5,071,173 to Hegler, et al. discloses a corrugated pipe joint having a coupling socket with an outer diameter substantially equal to the outer diameter of the corrugated pipe segments to be joined. To facilitate assembly of the joint, the joint of the Hegler, et al. patent provides a pipe having two sets of annular corrugations with different outer diameters. The conventional corrugations of the first set form the uniform outer diameter of the pipe segment. The second set of corrugations, which are spigot corrugations, have outer diameters smaller than the uniform outer diameter of the pipe segment and substantially equal to an inner diameter of the coupling socket. This is so that the coupling socket fits tightly over the spigot corrugations.
The smaller spigot corrugations are formed on the same equipment that the entire corrugated pipe segment is fabricated. Therefore, the finished pipe segment of the Hegler et al. patent cannot be selectively cut again to form shorter pipe segments. Furthermore, the Hegler et al. joint requires close tolerances between the joint components to create a tight fit, so that the outer diameters of the spigot corrugations must be substantially the same as the inner diameter of the coupling socket.